Mikael Peder

Validation of the cuff pedestal technique for rapid eye movement sleep (REMs) deprivation by electrophysiological recordings.

Twenty-four-hour recordings of electrophysiological correlates of the sleep-waking cycle in the rat were performed during different stages of cuff pedestal treatment. It was found that rats adapted to live on pedestals with the cuff raised displayed undisturbed patterns of sleep and wakefulness. Lowering the cuff for three days resulted in virtually total disappearance of rapid eye movement sleep (REMs), while slow wave sleep (SWs) was only slightly reduced. Raising the cuff induced a prominent rebound increase of REMs. These results accord with data obtained by means of the conventional flowerpot procedure and corroborate the validity of the cuff pedestal technique.

Effects of rapid eye movement sleep deprivation on regional brain metabolism as measured by 2-[14C]deoxyglucose autoradiography.

Regional brain metabolic activity of six male Sprague-Dawley rats was investigated with 2-[14C]deoxyglucose autoradiography. Regional brain metabolic activity was determined bilaterally for 60 brain structures, using laser densitometry. After 5 days of uninterrupted rapid eye movement sleep deprivation, increased metabolic activity was found in the lateral habenula, the caudal and middle parts of the limbic system, and in the corpus callosum.

Lighting Conditions Affect Testosterone Feedback Sensitivity in Castrated Rats

It has been shown in the Syrian hamster that a short photoperiod sensitizes the hypothalamo-hypophyseal axis of castrated animals to the negative feedback effect of testosterone. There is some evidence that even the reproductive system of the rat, which is generally considered not to be very sensitive to light, can respond to changes in illumination. Therefore, we found it of interest to examine whether alterations in lighting conditions produce changes of sensitivity in the negative feedback effect of testosterone in the rat. We kept intact, castrated, and castrated testosterone-treated animals either in periodic (L:D 12:12) or constant light for 7 days starting 4 weeks after castration. In all 3 testosterone-injected groups, serum luteinizing hormone (LH) was lower in constant than in periodic light. Exogenous testosterone did not decrease the castration-induced elevations of pituitary LH and follicle-stimulating hormone (FSH). On the contrary, testosterone increased the pituitary contents of LH and FSH, especially in constant light. We conclude that, in constant light, the hypothalamo-hypophyseal axis of the castrated rat becomes more sensitive to the negative feedback action of testosterone.

REM sleep deprivation increases early morning pineal melatonin in castrated rats.

Recently nighttime melatonin levels have been shown to be attenuated in depressive patients or patients with dementia of the Alzheimer type. On the other hand, depression can be transiently relieved by deprivation of rapid eye movement sleep. Since exogenous melatonin administration increases rapid eye movement sleep and slow wave sleep in the rat, could rapid eye movement sleep deprivation then inversely influence endogenous melatonin production? We found indices that in castrated Wistar rats 4 days of rapid eye movement sleep deprivation by the cuff pedestal method elevates the pineal content of melatonin by a factor of two at 1 to 2 h after light onset. Rapid eye movement sleep is thus suggested to influence pineal activity. This mechanism might be involved in the human depression-alleviating effect of rapid eye movement sleep deprivation.

Spectral Properties of Light Affect Plasma and Pituitary Gonadotropins in Male Rats

In order to find out whether different light spectra have any role in regulating the gonadotropin levels in male rats, we compared the 24-hour patterns of plasma and pituitary gonadotropins in rats kept for 7 days in natural or in cool white artificial lighting (exp. I). The intensity and periodicity of the two lighting conditions were adjusted as similar as possible. Further, we measured plasma and pituitary gonadotropins in the middle of the light period and in the middle of the dark period in rats kept for 7 days under artificial lightings of three different spectra (exp. II). In both experiments, in all lighting conditions we found higher plasma levels of LH and FSH during the dark than the light period. The differences were statistically significant only when the illumination contained more long and/or short wavelengths than the usual cool white laboratory lighting. The pituitary contents of gonadotropins were not found to vary with the periodicity of lighting. In the 24-hour patterns the overall plasma levels were higher and the pituitary contents of gonadotropins lower in natural lighting than in cool white lighting. It was concluded that the spectral properties of light influence the secretion of gonadotropins in male rats, but the mechanism involved remains to be clarified.

Rapid eye movement sleep deprivation affects sleep similarly in castrated and noncastrated rats

Twenty-four-hour recordings of electrophysiological correlates of the sleep-waking cycle in castrated and noncastrated Wistar rats were performed to validate the cuff pedestal technique in the deprivation of rapid eye movement sleep. An undisturbed pattern of sleep was found in both castrated and noncastrated rats when the cuffs were in the raised position. The lowering of the cuff for 4 days virtually abolished REMs in both groups of rats. During neither the dark nor the light period was there any difference between the castrated and noncastrated rats in the total amount of REMs rebound. The results accord with the data obtained by the conventional flowerpot procedure and show that castration does not influence the amount of REMs before, during, and after REMs deprivation in the rat. It is suggested that testicular testosterone, contrary to growth hormone, is not essential for the triggering of REMs sleep, although both have anabolic actions.

Rapid eye movement sleep deprivation depresses plasma FSH and LH in castrated rats

In castrated Wistar rats four days of Rapid Eye Movement sleep (REMs) deprivation by the cuff pedestal method induced decrements in plasma LH and FSH. The adenohypophyseal levels of these hormones were decreased in the REMs-deprived rats and in the control rats kept on pedestals with the supporting cuff in the elevated position as compared with the home-cage control rats. The results are discussed in terms of regional brain metabolic activity and transmission.

Effect of Neonatal Androgenization on the Testosterone Feedback Sensitivity in Adult Rats in Two Lighting Conditions

Neonatally androgenized and intact adult male Wistar rats received daily, during 1 week, either testosterone propionate or sesame oil injections in periodic or constant light. Serum and pituitary gonadotropins and hypothalamic LHRH were measured. In periodic light, neonatal androgenization did not change the serum concentration or pituitary contents of gonadotropins, or the hypothalamic content of LHRH. Testosterone injections decreased serum concentration and pituitary content of gonadotropin of intact rats but failed to decrease the pituitary gonadotropin content of neonatally androgenized rats. In constant light, serum FSH was decreased in neonatally androgenized rats. Testosterone injections decreased both serum LH and FSH concentrations of intact rats but only serum LH of androgenized rats. Pituitary gonadotropin and hypothalamic LHRH contents remained unchanged. We conclude that neonatal androgenization renders the male rat hypothalamo-pituitary axis more resistant to changes of testosterone concentration in adulthood. Constant light did not sensitize the neonatally androgenized rats to testosterone, but on the contrary, testosterone injections were less effective in constant than in periodical light.

Mouse-killing in Sprague-Dawley rats: Effects of lighting conditions

Sixteen male Sprague-Dawley rats were studied in artificial daylight and in red light for mouse-killing. Fifty percent of the rats killed mice. Killing varied, however, considerably: only seldom did it occur on consecutive days. More killing occurred during tests in red light than in artificial daylight. In red light, the mean latency between confrontation of the rat with the mouse and the killing was gradually shortened but not in daylight.

Little oscillation of daily food intake in mousekiller rats as opposed to nonkiller rats before any confrontation with mice

During 46 consecutive days the daily food intake and weight were recorded in 16 male Wistar rats. On Days 31-45 one mouse was presented each rat daily. Before any experience with mice (Days 0-27) the mousekiller rats, compared with the nonkiller rats, regulated their individual food intake more closely to their homeostatic equilibria, corrected for the linear trend. This result indicates a functional difference in food intake regulation between mousekiller rats and nonkiller rats prior to any experience with mice. However, no difference in the mean food intake was found between the mousekiller and the nonkiller rats.